In the present environment, an encoder system measures one or more operational attributes of an object (e.g., a rotary shaft, a printer head, a paper feeder). Examples of such operational attributes include the linear position of the object, the rotary position of the object, the speed of the object, and the like. In some existing encoder systems, measurement of one or more operational attributes of an object involves an emitter of the encoder system focusing light onto a codewheel or codestrip moving in conjunction with the object. The light is either reflected or not reflected to a receiver of the encoder system depending upon the “bar and window” pattern of the codewheel or codestrip. In existing reflective encoder systems, the “bar and window” pattern of the codestrip or codewheel consists of a repeating pattern of a non-reflective surface (i.e., the bar) and a reflective surface (i.e., the window). The total width of the non-reflective surface and the reflective surface is known as the grating period of the codewheel/codestrip pattern. As the codewheel or codestrip moves, an alternating pattern of light and dark corresponding to the pattern of the codewheel or codestrip falls upon the receiver. This collected light pattern is used to produce internal signals, which in turn are used to determine the earlier-mentioned measurements.
FIG. 1 depicts an exemplary prior art bar and window pattern for existing codestrips and codewheels. In FIG. 1, pattern 100 includes window 110 and bar 120. Bar 120 has a width w1. Likewise, window 110 has a width w2, thus creating a grating period of w1+w2. In some existing codewheels and codestrips, w1 is equal to w2. Moreover, for existing codestrips and codewheels, the value of w1, as well as that of w2, is usually greater than or equal to 1.6 μm to allow formation of part window patterns.
The precision of the aforementioned measurements depends upon the resolution of the codewheel or codestrip. The resolution of a codestrip is equal to the number of lines (i.e., bar and window pairs) formed by the codestrip per unit length of the codestrip (e.g., per inch, per mm, etc.). Furthermore, the resolution of a codewheel is equal to the counts per revolution (CPR) for the codewheel. The CPR for a codewheel may be determined using the following equation.CPR=LP×2πROPwhere LP=the number of lines per unit length (e.g., per inch, per mm, etc.); and                ROP=radius of the codewheel        
As can be seen from the above-equation, the resolution of a codewheel may be increased by increasing ROP, while keeping LP constant. However, size constraints for encoder systems may make increasing the size of the codewheel impractical.
Moreover, similar to earlier discussions, present techniques only allow so many bar and window pairs per unit length using existing codewheel or codestrip manufacture technologies (e.g., stamping windows into a codestrip or codewheel, printing opaque bars on the surface of a codestrip or codewheel, etc.). Therefore, increasing the LP of a codewheel or a codestrip to increase the resolution is also impractical. Using the maximum LP values, CPR values of up to 32, 768 have been achieved.